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APPEARANCE OF THE FRACTURE OF PIG IRON. 169
give the closer grained iron. All should perceive from this why the same kind of iron may have in one cast a close grain, and in another an open grain. As there are but few molders or founders who have ever had the opportunity of witnessing a furnace cast, 1 this explanation of its workings, combined with their own foundry experience, should assist many to realize why the fracture or hardness of pig metal is an unreliable guide to the iron's true grade.
As there are those who are still sure to contend that open pig fractures mean a soft iron and a close-grained iron a hard one, and if different results are obtained in castings to charge such to changes in fuel, scrap iron, fluxes, blast, weather, etc., the author has selected samples of pig iron shown in Figs. 37, 38, and 39, coming from two different casts, that are a fair representation of the whole cast or car of iron. If any of the old-school founders were asked to select from these a cast or car of iron to give soft castings, they would pick out iron such as sample A, seen in Figs. 37 and 39, while if they desire to make strong or hard castings they would select such irons as are represented by sample B, seen in Figs. 38 and 39. In fact, if they were asked to use such a cast or car of iron as that represented by B, they would claim that on account of its close grain and the blow-holes seen at D, the iron was hardly fit for sash-weights, let alone to think it of any value to make soft castings.
In order to convince the skeptical, or those not conversant with chemical analysis, or the effect of one metalloid upon another, that they are in error, the writer melted down about one hundred pounds of each of the grades A and B in his twin-shaft cupola, seenng the advance of the new, see page 179.n is simply an average of the whole, generally taken from the two ends andith the uncertainty of furnace workings when in urgent need of ten hundred jon of iron; and Sir........................ 2,720 "